I put cold bluing on them and then soak in bleach for about 10 minutes. When you take it out of the bleach it will be rusty. Just scotch brite it off and oil it good.
When you hot punch it will draw the temper even more. when I hot punch I will hit it a couple times and then dip the tip of the punch in water. This seems to help. Most all my punches are coil spring.
I have heard of using clear finger nail polish and painting the back and the hamon line in and then etching. I have never tried it so don't know for sure if it works
I do have to agree with Thomas,why fake it.